It is known in the art that the double bond in methyl 4-methoxybutenoates is stabilized more effectively by the methoxy group than by the ester. See, for example, Rhoads et al., J. Org. Chem., 35, 3352 (1970) and Hine et al., J. Org. Chem., 32, 2600 (1967).
Preparation of dehydroamino acids by elimination of HCl from an N-chloroamide is described by Poisel and Schmidt, Chem. Ber., 108, 2547 (1975).
U.S. Pat. No. 3,865,694 describes a fermentation process for preparing L-2-amino-4-(2-aminoethoxy)-trans-but-3-enoic acid. This material is also described by Pruess et al., J. Antibiot., 27, 229 (1974).
U.S. Pat. No. 4,014,898 describes the synthesis of compounds of the formula ##STR1## where R.sub.1 and R.sub.2 are lower alkyl; and R.sub.4 and R.sub.5, taken together with their attached nitrogen atom form the phthalimido group.
Similarly, U.S. Pat. No. 3,887,615 describes racemic and optically active compounds of the formula ##STR2## where R.sub.1 and R.sub.2, each independently, represent hydrogen or lower alkyl, or R.sub.1 and R.sub.2, taken together with their attached nitrogen atom form a 5- or 6-membered saturated heterocyclic ring wherein said 6-membered ring may contain an additional nitrogen atom or an oxygen atom; provided that one of R.sub.1 or R.sub.2 is other than hydrogen.